1. Field of the Invention:
This invention relates to a process and an apparatus which are used for manufacturing polymers.
2. Description of the Prior Art:
A known process for manufacturing polymers will be described by way of example with reference to the preparation of a solution of polyamide acid in an organic solvent as a precursor for polyimides which are used for a wide range of purposes including the manufacture of parts for electronic devices because of their good heat resistance and electrical insulating properties, and which are, therefore, required to be of high quality.
A solution of polyamide acid in an organic solvent has hitherto been prepared by adding a powder of dianhydride of an organic tetracarboxylic acid into a solution of an organic diamine in an organic solvent to cause them to react with each other, and stopping its addition when the growth in molecular chain of polyamide acid has resulted in a solution having a predetermined level of viscosity (several thousand poise). The polyamide acid which has been obtained is converted to polyimides which are used to form film, or the like.
The viscosity of the polyamide acid solution shows a logarithmic increase with the progress of reaction between the diamine and the dianhydride and finally reaches several thousand poise. As the final viscosity of the solution affects the properties of polyimides obtained by the conversion of polyamide acid, it is not allowed to differ from one lot of products to another, and must always be kept within a certain range. As the viscosity shows a logarithmic increase, however, the known process which employs the powder of dianhydride of an organic tetracarboxylic acid can hardly achieve the final viscosity controlled within a certain range and manufacture products of steady quality.
It is possible to lower the viscosity of the polyamide acid solution if an increased amount of organic solvent is employed. The use of an increased amount of solvent is, however, not only a disadvantage to the productivity of polyamide acid and polyimides obtained by the conversion thereof, but also results in a polyimide film of lower strength.
A detailed examination of products has revealed the presence of a variation in properties. This variation has been found to be due to the fact that the polyamide acid solution lacks uniformity. Although this may be a problem which can be overcome if the solution is carefully stirred in the reaction system, the uniform stirring of a fluid having a viscosity which is as high as several thousand poise requires a long time and is only possible at the sacrifice of productivity.
Moreover, polyimides and other polymers that are used for making parts of electronic devices, or the like are required to be of high quality, not containing any dust or other impurities. It has, however, been impossible to remove dust or other impurities from the powder of dianhydride of an organic tetracarboxylic acid. It has also been difficult to remove such impurities by filtration from the polyamide acid solution having a viscosity of several thousand poise. Therefore, the problem of removing impurities from polyamide acid has remained still to be solved.
These polymers contain numerous bubbles and these bubbles must be removed before the polymer is molded to form a product. It has hitherto been usual to remove bubbles from a viscous fluid, such as a plastic material, by placing the fluid in a tightly closed vessel and creating a reduced pressure in the vessel to allow the bubbles to expand and float to the surface of the fluid, so that they may eventually leave the fluid. However, this method, which relies upon the floating force of bubbles per se, requires an undesirably long time for the complete removal of bubbles and is only useful at the sacrifice of productivity. Moreover, bubbles are difficult to remove from that portion of the fluid which contacts the inner wall surface of the vessel, and the viscosity of the fluid is too high, and so it prevents the effective growth and movement of bubbles and therefore makes it impossible to remove bubbles unless a high vacuum is created in the vessel.
Although various problems have been pointed out in connection with the preparation of a polyamide acid solution as a precursor for polyimides, they also remain yet to be solved in connection with the preparation of other polymers that are required to be of high quality, particularly those which are prepared by the reaction of two substances in a solution formed by an organic solvent.